Coronary artery disease continues to be one of the leading causes of morbidity and mortality, throughout the world. The typical etiology of coronary artery disease is characterized by the build-up of atherosclerotic plaque within the coronary arteries. Such deposits of atherosclerotic plaque tend to fully or partially block the flow of blood through the affected coronary arteries, and if untreated can result in myocardial ischemica, infarction and death.
For many years, the traditional surgical treatment of coronary artery disease has been coronary artery bypass surgery. In traditional coronary artery bypass surgery, the patient is generally anesthetized and placed on cardiopulmonary bypass. A thoracotomy is performed and the obstructed coronary blood vessels are exposed by surgical dissection. One or more segments of the patient's saphenous vein or internal mammary artery is/are harvested for use as bypass graft(s). The harvested segment(s) of vein or artery is/are then anastomosed to the obstructed coronary artery(ies) to form bypass conduit(s) around the arterial obstruction(s). Such traditional coronary artery bypass surgery is expensive, extremely invasive, and is associated with significant operative and perioperative complications.
One alternative to traditional coronary artery bypass surgery is balloon angioplasty. In balloon angioplasty, a flexible guide catheter is percutaneously inserted into a peripheral artery (e.g., the femoral artery) and is transluminally advanced through the vasculature until the distal tip of the catheter is within an obstructed coronary artery. Thereafter, a balloon catheter is passed through the guide catheter and into the obstructive lesion. The balloon of the balloon catheter is inflated one or more times to dilate coronary artery in the region of the obstructive lesion. These balloon angioplasty procedures tend to be less expensive and less traumatic than traditional coronary artery bypass surgery. However, balloon angioplasty procedures of this type have been associated with a significant incidence of restenosis at the angioplasty site. The cause and mechanism of such restenosis continues to be the subject of ongoing study. However, such restenosis has generally been attributed to either a) an increase in the mass of the artery wall (e.g., neointima formation), b) a thickening of the artery wall without substantial change in it's mass (e.g., vascular remodeling) and/or c) radial contraction of the balloon-dilated artery wall upon healing of cracks and fissures that have been created by the balloon dilation process.
Another alternative to traditional coronary artery bypass surgery is transluminal atheroectomy or ablation of the obstructive matter within the coronary artery. These transluminal atheroectomy or ablation procedures are performed by passing a catheter-mounted ablation apparatus through the vasculature to the site of the coronary obstruction. the catheter-mounted ablative apparatus is then utilized to cut, shave, sonicate, pulverize or otherwise ablate the obstructive matter from the lumen of the coronary artery. These atheroectomy or ablative procedures must be performed with caution to avoid abrasion or damage to the artery wall, as such abrasion or damage can result in excessive scaring and subsequent reocclusion of the artery lumen. Furthermore, these atheroectomy or ablative procedures may, in some cases at least, be confounded by the need to meticulously contain and remove the severed fragments of obstructive matter in order to prevent such fragments of obstructive matter from escaping into the patient's circulatory system. Examples of such atheroectomy catheters and other catheter-mounted ablative apparatus are described in U.S. Pat. No. 3,433,226 (Boyd), U.S. Pat. No. 3,823,717 (Pohlman, et al.), U.S. Pat. No. 4,808,153 (Parisi), U.S. Pat. No. 4,936,281 (Stasz), U.S. Pat. No. 3,565,062 (Kuris), U.S. Pat. No. 4,924,863 (Sterzer), 4B70,953 (Don Michael, et al.), U.S. Pat. No. 5,069,664 (Suess, et al.), U.S. Pat. No. 4,920,954 (Alliger, et al.) and U.S. Pat. No. 5,100,423 (Fearnot), as well as foreign patents/patent publications EP0347098A2 (Shiber), WO87-05739 (Cooper), WO89-06515 (Bernstein, et al.), WO90-0130 (Sonic Needle Corp.), EP316789 (Don Michael, et al.), DE 3,821,836 (Schubert), DE2438648 (Pohlman), and EP 0443256A1 (Baruch).
Other alternatives to traditional coronary artery bypass surgery have included minimally invasive endoscopic procedures which, ostensibly at least, can be performed through small (e.g., 1-3 cm) incisions formed in the patient's chest wall, by insertion of a thoracoscope and associated operative instruments through such incisions. One such thoracoscopic coronary bypass procedure is described in U.S. Pat. No. 5,452,733 (Sterman et al.). If perfected, these minimally invasive coronary artery bypass procedures may lessen the discomfort and length of recovery time experienced by patients who undergo such minimally invasive procedures vis a vis those who undergo traditional coronary artery bypass surgery. However, the performance of endoscopic surgical procedures of this type typically requires a great deal of operator skill and training. Furthermore, as with traditional coronary artery bypass surgery, the patients on whom these thoracoscopic procedures are performed are likely to undergo general anesthesia (with or without cardiopulmonary bypass) and the creation of a pneumothorax due to the formation of full-thickness incision(s) in the chest wall. Thus, many of the drawbacks associated with traditional coronary artery bypass surgery, are also associated with these minimally invasive thoracoscopic procedures.
Another previously described procedure for bypassing coronary artery obstructions utilizes a transmyocardial passageway (e.g., an interstitial tunnel formed in the muscular wall of the heart) to carry blood from the left ventricle of the heart to an obstructed coronary artery. Such procedure, hereinafter generally referred to as “Transmyocardial Direct Coronary Revascularization” (TMDCR) is described in U.S. Pat. No. 5,287,861 (Wilk), U.S. Pat. No. 5,409,019 (Wilk), and U.S. Pat. No. 5,429,114 (Wilk). The TMDCR methods described in these prior patents require that a catheter be introduced into the obstructed coronary artery and advanced through the obstructive lesion. After the catheter has been advanced through the obstructive lesion, the distal tip of the catheter is directed toward the artery wall and an opening (i.e., a transmycardial passageway) is formed through the artery wall, through the adjacent myocardium, and into the chamber of the left ventricle. Also, in this previously described TMDCR method, a stent is required to be positioned within the transmyocardial passageway. Such intramyocardial stent is constructed to perform a one-way valving function (i.e., to open and close the transmyocardial passageway in accordance with changes in the systolic-diastolic cardiac cycle). These TMDCR methods, previously described in U.S. Pat. No. U.S. Pat. No. 5,287,861 (Wilk), U.S. Pat. No. 5,409,019 (Wilk) and U.S. Pat. No. 5,429,114 (Wilk), may be difficult or impossible to perform in patients who suffer from total or near total obstructions of a coronary artery, because of the necessary for advancing the catheter through the coronary artery obstruction to accomplish creation of the transmyocardial passageway at a location which is downstream of the coronary obstruction. Furthermore, because these previously described TMDCR methods require placement of a stent within the transmyocardial passageway, such procedures are necessarily associated with procedural complexities associated with measuring and precutting the stent to a precise length so that it fits within the transmyocardial passageway without protruding into the chamber of the left ventricle and/or the lumen of the coronary artery. Also, any stent which is positioned solely within the transmyocardial passageway may be subject to repetitive flexing and/or stressing as the myocardium undergoes its normal contraction and relaxation. Such repeated flexing and/or stressing of the intramyocardial stent may lead to unwanted migration, dislodgement or damage of the stent.
In view of the above-summarized shortcomings and complexities of the previously described TMDCR methods, there exists a need in the art for the development of improved TMDCR methods and associated apparatus which may be utilized without the need for cumbersome stenting of the transmyocardial passageway and/or implantation of one-way valving apparatus within the transmyocardial passageway. Also, there exists a need for the development of a new TMDCR methods which can be performed in patients who suffer from total or near total coronary artery occlusions, without the need for advancing a catheter through such coronary artery occlusion(s).